1. Field of the Invention
The present invention relates to a high voltage cabtire cable to be used for power feeding for mobile devices, more particularly, to a high voltage cabtire cable in which adhesion property between power cores and other cores is improved when the power cores and other cores are coated with an inner sheath.
2. Related Art
The “cabtire cable” is also called as “cabtyre cable”, the name of which is derived from “cab tire”, since this kind of cables are as tough as “car tires” in mobile application. The “cabtire cable” is a kind of a flexible cable e.g. a rubber-sheathed flexible cable in which a core such as power core is coated with an insulation and further jacketed with a flexible but tough material such as hard rubber.
The high voltage cabtire cable is formed by stranding (twisting) a plurality of power cores and other cores, coating outer peripheries of the stranded power cores and other cores with an inner sheath, and jacketing the coated cores with an outer sheath. Recently, as the other cores to be stranded (twisted) together with the power cores, an optical fiber unit for use in communication control is stranded (twisted) together as well as grounding cores.
The power core is formed by providing an insulation around a conductor. For achieving electric characteristics stability, conductive layers (semi-conductive layers) are provided around the conductor and the insulation respectively. Namely, the conductive layers (semi-conductive layers) are provided between the conductor and the insulation, and on the insulation. Materials and characteristics of respective conductive layers are varied depending on the kind of the cabtire cable and its service voltage. In general, a semi-conductive fabric tape, extrusion-type semi-conductive rubber, extrusion-type semi-conductive plastic, etc. are used as the conductive layer.
This type high voltage cabtire cable is used for high voltage power supply to the mobile devices such as crane and elevator. The high voltage cabtire cable is used in a severe environment, in which the cable is subjected to inflection and twisting as well as strokes and frictions in a pulley or reel, etc. repeatedly.
Accordingly, it is preferable that the insulation and the semi-conductive layer (hereinafter referred to as “inner semi-conductive layer”) provided directly around the conductor of the power core are bonded strongly to each other for the use of the cabtire cable. In general, there will be no problem if the inner semi-conductive layer and the insulation are made from similar materials (i.e. materials in the same series). The inner semi-conductive layer is formed by a method of winding a tape including a base fabric of staple fiber coated with conductive butyl rubber, or a method of extruding semi-conductive EP rubber (EPR: Ethylene Propylene Rubber), semi-conductive butyl rubber (IIR: Isobutylene-Isoprene Rubber), or the like.
On the other hand, for a semi-conductive layer to be provided on the insulation of the power core (hereinafter referred to as “outer semi-conductive layer”), appropriate adhesion property (i.e. adhesion force) and appropriate separation property (generally called as “free-strip property”) are required with considering electrical characteristics and easiness in terminal processing when using the cable. Accordingly, the semi-conductive layer provided by extrusion is selected rather than a semi-conductive layer provided by winding the tape.
Japanese Patent Laid-Open No. 6-52728 (JP-A 6-52728) proposes the use of nitrile rubber (NBR: Nitrile-Butadiene Rubber) as a base resin composition for a semi-conductive layer used as the outer semi-conductive layer.
Japanese Patent Laid-Open No. 2008-21456 (JP-A 2008-21456) discloses a high voltage cabtire cable in which an inner sheath made of a blended material of chlorinated polyethylene (CM, also called as CPE), ethylene copolymers, and EP rubber, and an outer sheath made of a chloroprene rubber (CR) are provided. In JP-A 2008-21456, only a plurality of power cores are stranded together.
Further, in a cable configuration in which the power cores as well as other cores such as a grounding core and an optical fiber unit are stranded together, the same material as that of the outer semi-conductive layer, i.e. the NBR based conductive material is used for a coating material of the grounding core, so as to reduce a grounding resistance. Still further, as a material for a sheath of the optical fiber unit, materials having required properties for maintaining desired characteristics are selected appropriately.
On the other hand, as to materials for an inner sheath and an outer sheath for coating a stranded core formed by stranding the power cores, the grounding cores, the optical fiber unit and the like, characteristics such as abrasion-resistance property, oil-proof property, high hardness are compatibly required. Therefore, a base material such as chloroprene rubber (CR), chlorinated polyethylene (CM), chlorosulfonated polyethylene (CSM), etc. are generally used for the material of the inner or outer sheath.